The present invention relates to a suspension system for a vehicle, and more specifically to a stabilizer bar that can be selectively decoupled.
Vehicles are commonly equipped with independent suspension systems for absorbing road shock and other vibrations while providing a smooth and comfortable ride for the vehicle occupants. In suspension systems of this type, a stabilizer bar is often used to increase the roll rigidity and improve the steering stability of the vehicle.
Typically, the stabilizer bar is an elongated member oriented to extend laterally across the vehicle with a first and second segment extending longitudinally at each end of the central segment. The central segment of the stabilizer bar is supported for rotation about its own longitudinal axis by one or more mounting brackets which are fixed to the vehicle body or frame. Each longitudinal segment is attached to a suspension member such as a control arm of the suspension system by an end link.
When the vehicle is subjected to a lateral rolling force such as, for example, while the vehicle negotiates a turn, the longitudinal segments pivot in opposite directions with respect to the longitudinal axis of the central segment. As a result, torsional reaction forces are generated which act through the segments to urge the suspension members to move toward their normal position. Thus, the vehicle body will be prevented from excessive rolling or leaning to either side by the torsional resistance produced by the stabilizer bar.
A relatively large diameter stabilizer bar offers greater resistance to roll than a relatively small diameter bar. A drawback of a large diameter stabilizer bar is that while roll resistance is improved, ride quality decreases as an impact harshness of wheel disturbances from road inputs is increased. A relatively small diameter stabilizer bar inputs less impact harshness to a vehicle, but does not provide as much roll resistance.
Although desirable from a handling perspective, the effect of a stabilizer bar can be undesirable when the suspension system is subjected to a sharp input force, such as when one wheel of the vehicle strikes a curb, pothole or the like. Because the stabilizer bar transmits the input from one wheel to the other, suspension system harshness is increased and both sides of the suspension system can be subjected to an extreme articulation. This is undesirable from a handling and maintenance perspective.
In one known system a primary stabilizer bar of small diameter is selectively increased in diameter by adding secondary torsional reaction segments. The secondary torsional reaction segments includes a clutch system to engage the various secondary segments with respect to each other and with the primary segment. However this known system requires relatively large diameter segments to be shifted along the primary segment to modify the torque reactive capacity of the primary reaction segment. Shifting of the large diameter segments requires a relatively long period of time which thereby reduces the reaction time of the suspension system. Further, movement of the large diameter segments requires a large actuator assembly which increases suspension system weight.
It is desirable to provide a lightweight stabilizer bar system having the roll resistance of a large diameter bar with the low impact harshness found in a small diameter bar or in a vehicle without a stabilizer bar. It would be particularly desirable to provide a stabilizer bar system which can quickly react to changes in road condition to provide immediately adaptable handling and ride characteristics.
The suspension system according to the present invention provides a stabilizer bar having a decoupler assembly. The suspension system includes a stabilizer bar having a central portion attached to a first and a second segment which is attached to respective vehicle suspension members by an end link.
The central portion includes a decoupler assembly. The decoupler assembly selectively allows for the coordinated or uncoordinated movement of the first and second segments. The decoupler assembly is preferably in communication with a controller and sensors located adjacent the vehicle wheel assemblies. The controller interprets the signals from the sensors and determines whether the decoupler assembly should be activated and to what degree.
A first embodiment of the decoupler assembly provides an electromechanical clutch assembly. Preferably, the electromechanical clutch assembly coordinates the first segment and second segment motion up to a predetermined input preferably optimized for normal driving conditions. However, when one of the segments is subjected to a force above the predetermined input, such as a curb impact, the decoupler assembly selectively decouples the first segment from the second segment. Shock resulting from the curb impact is thereby prevented from being transferred from the first segment to the second segment.
In another embodiment, the electromechanical clutch may be operated in a limited slip manner preferably in communication with the controller and sensors. The controller interprets the signals from the sensor and determines the degree to which the decoupler assembly should be activated. In response to the controller""s interpretation of a signal from the sensor, the controller activates the decoupler assembly to provide a limited slip between the normally coordinated motion of the first and second segment. Variable activation of the decoupler assembly is thereby provided.
In another embodiment the first segment is coupled to the second segment by a piezo-electric coupling system. Under normal driving conditions a ring of piezo-electric material grips the male coupling and coordinates motion between the first segment and second segment. When the vehicle strikes a pothole or the like, the sensor identifies the force exerted upon the suspension member. The controller interprets the signals from the sensor and determines the degree to which the decoupler assembly should be activated. For example, if a relatively large pothole is struck, the controller will interpret a relatively high signal from the sensor and apply a first predetermined electric field through the ring of piezo-electric material such that the ring of piezo-electric material relaxes its grip on the male coupling. The first segment and second segment are thereby decoupled and the resulting shock is prevented from being transferred from the first segment to the second segment.
In another embodiment of the decoupler assembly, the first segment is coupled to the second segment by a magnetic coupling system. In this disclosed embodiment, a female coupling is electro-magnetically engageable with a male coupling. The female coupling is attached to the second segment and the first segment is attached to a male coupling. As described above, the controller interprets the signals from the sensor and determines the degree to which the decoupler assembly should be activated.
In yet another embodiment of the decoupler assembly, the first segment is coupled to the second segment by a solenoid decoupling system. In this disclosed embodiment, a receipt member is electro-magnetically engageable with a movable plunger. The movable plunger is attached to the second segment and the first segment is attached to receipt member. As described above, the controller interprets the signals from the sensor and determines the degree to which the movable plunger engages the receipt member.
Accordingly, the present invention provides a lightweight stabilizer bar system which can quickly react to changes in road condition to provide immediately adaptable handling and ride characteristics.